In railway couplers utilized by the American Association of Railroads, coupling of cars is achieved by means of interlocking knuckles pivotally carried on coupler heads by knuckle pins. The coupler heads are relatively massive castings connected to the undercarriages of railway cars and cannot be readily replaced. The knuckles, however, can be easily replaced by removing their associated knuckle pins. Consequently, if a failure (i.e., casting fracture) should occur in the coupler due to fatigue or stress, it is desired that it occur in the easily-replaceable knuckle rather than the coupler head.
It will be appreciated that inter-locking coupler knuckles can be in either compression or tension, depending upon the direction of movement of a train. When movement of a train reverses, the knuckles change from a tension condition to a compression condition; and the nose of each knuckle tends to slam into the throat portion of the other. After a period of time, this results in a metal fatigue condition with attendant cracks in the throat region of the knuckle, causing the knuckle to eventually fail in the throat region. Failure can also occur in the pin itself due to bending loads imposed on the pin upon movement of a train from a stopped position as well as when the train reverses direction. Other conditions which occur during the use of railway couplers bring about repetitive stress loadings on a knuckle pin; and these loadings can eventually cause the pin to fail. Thus, in prior art couplers, failure usually occurs in the knuckle pin itself or in the throat region of the knuckle rather than in the relatively massive coupler head.
In the past, failure of the knuckle usually occurred in the throat or around the knuckle pin hole due to the fact the kidney core used to produce a hollow cavity in the knuckle tail during casting was anchored by a projection into an enlargement of the pin hole core, producing a point of weakness. Previous designs, however, did not give sufficient support to the pin itself, resulting in the possible premature failure of the pin due to fatigue as explained above.
In U.S. Pat. No. 4,640,422 issued to William O. Elliott, a system is described for correcting knuckle pin failure problems. This is achieved by supporting at least a part of the knuckle pin along its length between the top and bottom of pin support walls of the knuckle. This can be achieved by forming an annular rib which projects into the core area of the knuckle about midway between the top and bottom pin support walls of the knuckle, or by a continuous pin-support wall extending along the height of the knuckle; with the pin receiving opening in the wall dimensioned to restrain the pin against lateral bending. In order to achieve this desirable result, however, it becomes necessary to modify the kidney core used to produce the hollow cavity in the knuckle tail such that it no longer projects into and is supported on the core for the pin hole itself. While the system shown in the aforesaid U.S. Pat. No. 4,640,422 is entirely satisfactory for its intended purpose, it does produce a condition wherein the knuckle is strengthened and will not fracture before a possible fracture of the coupler head itself. That is, the knuckle will no longer fracture and will not fail along the throat or pin hole portion.